knocking diesel engine

[Roverron]

Originally Posted by COLVERT

Thanks for your reply Ron. The first paragraph I find interesting. I guess the ECU must compensate for variable pressure up to around 3,000 rpm by holding the injectors open that fraction longer:

The injector opening time is just what it needs to be to either maintain a constant speed or provide whatever demand the driver is requesting via the accelerator. So the ecu doesn't compensate as such, its just programmed to proved a given quantity of fuel and as it knows the pressure, can work out the duration.

Hence tuning boxes work by increasing the pressure, though as the ecu isn't aware of this, it doesn't reduce the duration, so more fuel is injected and thus more torque produced.

The reason the fuel pressure is not constant is because the HP pump consumes a significant amount of power, so the pressure is only as high as it needs to be to provide the torque and meet emissions tests.

Returning to the subject of injector cleaning by means of an Italian Tune-up, there's many a car passed its MOT after being given a good blast up the road with some injector cleaner in the fuel. Thata's not an old wives' 'tale, its a fact.
I believe that diesels that are always driven gently will suffer from clogged injectors, cats, exhaust, even egr valve much more so than cars driven hard.
I recommend everyone give their diesel a good thrashing once a month to clear it out. You are not doing your engine any favours by being a gentle driver!

Ron